Magnetic field sensors can be used in a variety of applications. In one application, a magnetic field sensor can be used to detect a direction of a magnetic field, i.e., and angle of the direction of the magnetic field. In another application, a magnetic field sensor can be used to sense an electrical current. One type of current sensor uses a Hall Effect magnetic field sensing element in proximity to a current-carrying conductor.
Planar Hall elements and vertical Hall elements are known types of magnetic field sensing elements used in magnetic field sensors. A planar Hall element tends to be responsive to magnetic field perpendicular to a surface of a substrate on which the planar Hall element is formed. A vertical Hall element tends to be responsive to magnetic field parallel to a surface of a substrate on which the vertical Hall element is formed.
Other types of magnetic field sensing elements are known. For example, a so-called “circular vertical Hall” (CVH) sensing element, which includes a plurality of vertical Hall elements, is known and described in PCT Patent Application No. PCT/EP2008056517, entitled “Magnetic Field Sensor for Measuring Direction of a Magnetic Field in a Plane,” filed May 28, 2008, and published in the English language as PCT Publication No. WO 2008/145662, which application and publication thereof are incorporated by reference herein in their entirety. The CVH element is a circular arrangement of a plurality of vertical Hall elements arranged over a common circular implant region in a substrate, and without barriers to flow of electrical current among the vertical Hall elements. The CVH element can be used to sense a direction (i.e., an angle) (and optionally, an amplitude) of a magnetic field in a plane of the substrate.
Various parameters characterize the performance of magnetic field sensing elements and magnetic field sensors that use magnetic field sensing elements. These parameters include sensitivity, which is a change in an output signal of a magnetic field sensing element in response to a change of magnetic field experienced by the magnetic sensing element, and linearity, which is a degree to which the output signal of the magnetic field sensing element varies in direct proportion to the magnetic field. These parameters also include an offset, which is characterized by an output signal from the magnetic field sensing element not representative of a zero magnetic field when the magnetic field sensing element experiences a zero magnetic field.
The above-described CVH element is operable, with associated circuits, to provide an output signal representative of an angle of a direction of a magnetic field. Therefore, as described below, if a magnet is disposed upon or otherwise coupled to a so-called “target object,” for example, a camshaft in an engine, the CVH element can be used to provide an output signal representative of an angle of rotation of the target object.
The CVH element provides output signals from a plurality of vertical Hall elements from which it is constructed. Each vertical Hall element can have an undesirable and different DC offset.
The CVH element is but one sensing element that can provide an output signal representative of an angle of a magnetic field, i.e., an angle sensor. For example, an angle sensor can be provided from a plurality of separate vertical Hall elements or a plurality of magnetoresistance elements.
A CVH element has an operation limit at which it can sample vertical Hall elements in the CVH element to identify a direction of the magnetic field. The limit is related to how fast electronic circuits coupled to the CVH element, i.e., how fast a CVH magnetic field sensor that has a CVH element, can take sequential samples around the ring of vertical Hall elements, e.g., thirty-two or sixty-four vertical Hall elements. This limit is of particular interest when the magnetic field is rotating. In order to accurately identify a direction of a rotating magnetic field, a rate at which the CVH magnetic field sensor sequentially samples all the vertical Hall elements of the CVH element must be much higher than the rate of rotation of the magnetic field. It would be desirable to provide a magnetic field sensor forming an angle sensor that can operate at higher sampling rates and that can sense a more rapidly rotating magnetic field.
In addition, using, for example, sixty-four vertical Hall elements in a CVH element and a non-rotating magnetic field, a basic angular resolution is about 5.6 degrees (three hundred sixty divided by sixty-four). It would be desirable to provide a magnetic field sensor forming an angle sensor with a higher resolution (i.e., a smaller basic angle of resolution.)